Working length determination

Working length determination

1. Prepared by
Dr . Hamed Mohammed AL- Haddad
1

2. Working Length Determination
. The cleaning, shaping, and obturation of the
root canal system cannot be accomplished
accurately unless the working length is
determined precisely.
2

3. Definition:
Working length is defined as the distance from a coronal
reference point to the point at which canal preparation
and obturation should terminate.
3

4. REFERENCE POINT
The reference point is the site on the
occlusal or incisal surface from which
measurements are made. This point is
used throughout canal preparation
and obturation.
4

5. ٍSelection of Reference point
A reference point is chosen that is stable and
easily visualized during preparation. Usually
this is the highest point on the incisal edge on
anterior teeth and a buccal cusp tip on
posterior teeth. The same reference point is best
used for all canals in multirooted teeth. The
mesiobuccal cusp tip is
preferred in molars.
5

6. Stability of Reference Point
. Reference Point should not change between the
appointments.
. Don’t use weakened enamel walls or diagonal lines of
fracture as a reference site for Length – of – tooth
measurement.
. Weakened cusps or incisal edges are reduced to a well –
supported tooth structure.
Areas other than cusp tips, such as marginal ridges or the
floor of the chamber, are unreliable or difficult to
visualize.
6

7. . Diagonal surfaces should be flattened to give an accurate
site of reference.
7

8. Anatomic apex: Is the tip or the end of
the root determined morphologically,
whereas the


8

9. radiographic apex is the tip or end of the
root determined radiographically.


9

10. Apical Constriction: (minor apical diameter(
. It is the apical portion of the root canal
having the narrowest diameter. This
position may vary but is usually O,5 to 1.0
mm short of the center of the apical
foramen.

10

11. Apical foramen: Is the main apical opening of
the root canal. It is frequently eccentrically
located away from the anatomic or
radiographic apex.


11

12. . The minor diameter widens apically to the

foramen (major diameter).
12
1212

13. Clinical Considerations
. Before determining a definitive working
length, the coronal access to the pulp
chamber must provide a straight
pathway into the canal orifice.
. Loss of working length during cleaning
and shaping can be a frustrating
procedural error.
13

14. . It is extremely important to monitor the
working length periodically since the
working length may change as a curved
canal is straightened.
. The loss may also be related to the
accumulation of dentinal and pulpal
debris in the apical area .
14

15. . Loss of working length may also be due to
ledge formation or instrument
separation and blockage of the canal.
. Most dentists agree that the desired end
point is the apical construction, which is
not only the narrowest part, but a
morphological Land – Mark that can help
to improve the apical seal.
15

16. . If the length being too long, this may lead to
perforation through the apical construction,
with subsequent overfilling or overextension,
which mean postoperative pain, prolonged
healing period.
. Incomplete cleaning and filling may cause
persistent discomfort, also apical leakage may
occur into the uncleaned and unfilled space
short of the apical constriction.
16

17. TECHNIQUE & Methods FOR W- L
DETERMINATION
There is Different techniques have been
used, studied , and advocated for
determining working length
1- Radiographic method
2-Electronic method
3-tactile methods
17

18. Determination of Working Length by
Radiographic Methods
. This method is known as the Ingle method,
which proved to be superior to others.
. It showed a high percentage of success with a
smaller variability. This method first
proposed more than 40 years ago, and
become the most commonly used method.
18

19. Radiographic Apex Location: The following
items of materials and conditions are
essential to perform this procedure:

1. Good, preoperative radiographs showing
the total length and all roots of the
involved tooth.
2. Adequate coronal access to all canals.
19

20. 3. An Endodontic millimeter ruler.
4.Working knowledge of the average
length of all the teeth.
5. A definite, repeatable plane of
reference to an anatomic landmark on
the tooth.
20

21. . To establish the length of the tooth, a
stainless steel reamer or file with an
instrument stop on the shaft is needed.
21

22. . The instrument site must be small enough to
negotiate the total length of the canal but large
enough not to be lose in the canal.
No. 8 or 10 files should not be used to take
working length radiographs; small file tips
fade out and are usually not visible. On molar
radiographs, No. 15 file tips are often obscure.
22

23. 23
1. Measure the tooth on the preoperative
radiograph.

24. 2. Subtract at least 1.0mm " safety allowance " for
possible image distortion.
3. Set the endodontic ruler at this tentative working length
and adjust the stop on the instrument at that level.
24

25. 4. Place the instrument in the canal until the
stop is at the plane of reference unless pain
is felt (if anesthesia has not been used), in
which case, the instrument is left at that
level and the rubber stop readjusted to this
new point of reference.
25

26. 5. On the radiograph, measure the difference
between the end of the instrument and the
end of the root and add this amount to the
original measured length the instrument
extended into the tooth.
26

27. 6. From this adjusted length of tooth, subtract
a 1.0mm "Safely factor" to conform with
apical termination of the root canal at the
apical constriction.
7. Set the endodontic ruler at this new
corrected length and readjust the stop on
the exploring instrument.
27

28. 28

29. 8. When the length of the tooth accurately
confirmed, reset the endodontic ruler at
this measurement.
9. Record this length and the coronal point of
reference on the patients record.
29

30. 10. It is important to emphasize that the
final working length may shorten by as
much as 1mm as a curved canal is
straightened out by instrumentation. It
is therefore recommended that the
"length of the tooth" in a curved canal
be reconfirmed after instrumentation
is completed.
30

31. Modification of length
substraction in case of Resorption
Working length distance from the apex is
determined when the following are seen
radiograpbically:
1. No bone or root resorption: 1 mm from
apex.
2. Bone but no root resorption: 1.5 mm from
apex.
3. Bone and root resorption: 2 mm from apex.
31

32. 32

33. Electronic Method by Using
Electronic Apex Locators
33

34. Principle of measuring by Using
Electronic Apex Locators
34
A root canal instrument is connectedto the
measuring device with aclip. An electric current is
passed through the file into the root canal. A lip
or hand electrode serves as the opposite electrode.
The device indicates the apical foramen by an
absolute resistance value that is presented by the
manufacturer. Currents alternating at different
frequencies minimize the influence of
electrochemical polarizing processes

35. Principle of measuring by Using
Electronic Apex Locators
35

36. Tactile Methods
tactile methods are too unreliable.
Radiographs are usually made to
determine the working length
36

37. Tactile Methods
There are problems with this approach
also. First, the procedure is painful for the patient.
Second, a necrotic pulp frequently contains
vital inflamed tissue that extends several
millimeters into the canal . This tissue may be very
sensitive and respond to instrument contact short
of the apex.
Third, a patient feels pain after canal
preparation is complete from hydraulic pressure
even though instruments do not reach the apical
region.
37

38. Tactile Methods
The opposite of pain with instruments short of
length is lack of pain response when instruments
are beyond the apex. This has been observed in
some situations when, in an unanesthetized patient,
an instrument has passed several millimeters
out of the apex without being detected
38

39. Determination of Working Length by
Paper Point Measurement
. In a root canal with an immature (wide open) apex, the
most reliable means of determining working length is
to gently pass the blunt end of a paper point into the
canal.
. The moisture or blood on the portion of the paper point
that passes beyond the apex may be an estimation of
working length.
39

40. Determination of Working Length by
Paper Point Measurement
40

41. . This paper point measurement method is a
supplementary one.

. A new dimension has recently been added to
paper points by the addition of millimeter
markings. These paper points have
markings at 18,19,20,22 and 24mm from the
tip.
41

42. . The accuracy of these markings should be
checked an a millimeter ruler.
42